Portable modem



FIG. 1 is a perspective view of an ornamental design for a portable modem;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a first side view thereof;

FIG. 5 is a second side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken line in FIGS. 1-7 showing environmental structures is for illustrative purposes and forms no part of the claim design. 

The ornamental design for a portable modem, as shown and described. 